I don't know if "direct swap" is the word I would use. You're referring to the entire front end, not just the forks. Forks, triples, wheel, brakes, possibly clip ons, etc. When you get into that level of swap, almost any bike can be made to work, with varying amounts of modification required.

OP, move along from 03-04 600RR forks. If you want to upgrade, get 929/954 front, or 05+ RR front with the inverted forks. There's no upgrade from using 03-04 forks instead of F4i. But also, as mentioned, simply upgrading and correctly setting up F4i internals would give you the same results without extra modification.

 

I'd say thats debatable honestly. The RR conventional forks are 2mm larger diameter [more rigid, the entire point of inverted forks] and the brake rotors are slightly larger as well. I completely agree they are not in any way worth the effort or expense to swap though.

 

True, they are thicker in diameter. But you're still using old tech, since they are not inverted. If you're going to do a swap, do it with better parts.